The present invention relates to a machine tool equipped with a rotary table, and to a method for computing the attachment position of a balancer with respect to the rotary table.
A typical machine tool equipped with a rotary table is designed such that the rotary table is linearly moved forward and backward, and rotated. A workpiece attached to the rotary table is, for example, cut by a tool provided on a tool post.
Depending on the attaching state of a workpiece or a jig on the rotary table, a rotational imbalance may be caused on the rotary table. If such a rotational imbalance is caused, the rotary table vibrates. When a turning process is performed in this state, the workpiece becomes defective. In some cases, the rotary table might get broken, or the workpiece might be detached from the rotary table.
Therefore, a vibration sensor for detecting vibration of the rotary table may be provided on the rotary table. In this case, when the rotary table causes vibration due to the rotational imbalance, an operator is informed of the situation. However, since informing the operator of the situation does not eliminate the rotational imbalance, the problem caused by the rotational imbalance is not fundamentally solved.
Japanese Laid-Open Patent Publication No. 2002-28858 discloses a machine tool that causes a tool post equipped with a rotary tool to move forward and backward with respect to a workpiece. The machine tool includes a servo system that controls a linear motor that moves the tool post forward and backward with respect to the workpiece, and disturbance predicting means that predicts a disturbance that the rotational imbalance of the rotary tool causes to act on the servo system. The servo system is controlled to compensate for the influence of the disturbance predicted by the disturbance predicting means.
More specifically, based on a current command value output from a speed feedback loop of the servo system, and a position feedback value output from a position detector, which detects the position of the tool post, the disturbance that the rotational imbalance of the rotary tool causes to act on the servo system is predicted. In accordance with the predicted disturbance, a current command value entered to a current feedback loop of the servo system is corrected, compensating for the influence of the disturbance. As a result, the speed fluctuation of a grinding head caused by the rotational imbalance of the rotary tool is suppressed, which improves the machining accuracy of the workpiece.
However, the technique disclosed in the above publication is for suppressing the speed fluctuation of the grinding head, and does not eliminate the rotational imbalance of the rotary tool. Thus, even if the technique disclosed in the above publication is applied to the machine tool equipped with the rotary table, the rotational imbalance of the rotary table is not suppressed, and problems such as damage to the rotary table or detachment of the workpiece are not solved.